The invention relates to a carburetor including a main housing portion, in which a Venturi tube and a throttling port are defined and which has an air intake side and an engine exit side, which comprises a fuel pump, a fuel intake feed channel for supplying fuel from the fuel pump to a dosing chamber, a throttle valve arranged in the throttling port between the air intake side and the engine exit side, the dosing chamber for supplying fuel from the fuel pump into the Venturi tube or the throttling port through a main exit port and at least one slow-speed exit port. The main exit port at the air intake side of the throttle valve ends in said Venturi tube. The carburetor further includes: throttle supply passage which comprises an inlet port and an outlet port, the inlet port being in a direct fluidic connection with the fuel intake feed channel, the outlet port being in a direct fluidic connection with said throttling port and the inlet port being in a direct fluidic connection with said outlet port. A means for selectively opening and closing said throttle supply passage is typically provided, and the outlet of the throttle supply passage ends in upstream direction of the throttle valve, as is known from the EP 0 287 366 B1.
It has become known to provide a return fuel line which with its one end is connected to the fuel feed line and with its other end is connected to the fuel tank and including a throttle therebetween (EP 0 464 673 A1).
Such a carburetor, with or without a return fuel line which is provided with a flow resistance, typically cannot be combined with a closed pressure-sealed tank. Today, however, it is desirable and partly a condition of sale to provide a fuel tank that is impermeable to an efflux of gas (fuel-air mixture) in order to reduce the environmental load, especially also with respect to storing the device. For this purpose, the tank is manufactured so that it is completely closed and is only provided with a suction relief valve connected to the outside (atmosphere) which suction relief valve opens for allowing outer air to get in when taking fuel from the tank. However, when using such a closed tank, a flooding of the carburetor takes place in case of a temperature rise and a corresponding increase of pressure in the tank, if e.g. the needle valve of the diaphragm control does not close reliably or the choke valve is opened.
The direct lead of the fuel from the fuel intake feed channel to the Venturi or throttle valve area, with the control being opened, may very easily result in a flooding of the carburetor in case of a pressure build-up.